Wüest M. 51 Wykes M. 82 Yamaguchi M. 17 Ybarra G. 129 Yubero F ...

JUNE 28 WEDNESDAY AFTERNOON
RIVA-SS-WeA-P.2 SECONDARY ELECTRON EMISSION YIELDS OF EXTER-
NAL DIELECTRIC COATINGS USED IN SPACE . Isabel Montero, Ainhoa Pardo, Pablo
Rios and José Luis de Segovia. Instituto de Ciencia de Materiales de Madrid. CSIC. Cantoblanco.
28049-Madrid. Spain. Luis Galán. Universidad Autónoma de Madrid. Cantoblanco. 28049-Madrid.
Spain. Léon Lévy. Office National d'Etudes et de Recherche Aerospatiales, 2 Avenue Edouard Belin,
31055 Toulouse, Cedex 4, France. Marc Van Eesbeek. European Space Research and Technology
Centre (ESTEC), European Space Agency (ESA), Keplerlaan 1, PO Box 299, NL-2200 AG Noordwijk,
The Netherland
Within ESA Program, AO4136 “Material Characterisation for Plasma Interaction Analysis”, headed
as prime contractor by ONERA, our group from ICMM (CSIC) and UAM has been developing a research
on secondary electron emission and photoemission properties of reliable insulator materials to
study their charging behaviour in space.
The spacecraft surface potential is a function of the net current flow to or from the spacecraft surface.
Electrons impinging on the spacecraft can produce secondary electron emission. Photoemission
from the extreme ultraviolet photon range is the most important since in that region many materials
have rather large photoelectric yields and the solar spectrum also has significant energy there. This
work presents results on secondary electron emission and photoemission yields of space used external
dielectric coatings. The dielectric materials studied was polymers: kapton, betacloth and upilex,
and doped silicon glasses: CMX and CMO.
The total secondary electron emission coefficient, σ, per primary electron, versus primary energy,
Ep, curve was characterized by the following parameters: σm the maximum value and the corresponding
primary energy Em, and the two crossover energies: E1, the lowest Ep for σ =1, and E2 the
highest Ep for σ =1. The beam pulsing measuring technique was used in order to reduce or avoid the
charge incorporation into the samples. SEY was measured for normal incidence and as a function of
primary electron energy. Current pulses of 0.1 -1 μs of low intensity (1nA-50 nA) were used to reduce
the electron dose received by the sample (≤106electrons/pulse). For each primary energy, the
sample was bombarded with only one current pulse. Surface charge decay occurs immediately when
the e-irradiation is stopped, but it depends on the discharging time constants. After each measurement,
the charge of the sample was removed: the trapped charge was liberated with the mercury
lamp (negative surface charging) and the flood-gun (positive surface charging). Analysis of the coatings
was performed, apart from SEY and PES measurements, by XPS (X-ray Photoemission Spectroscopy),
SEM (Scanning Electron Microscopy), EDX (Energy Dispersive X-ray Spectroscopy) and
UVS (Ultraviolet spectroscopy).
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